Magnetron tunable by piezo-electric means over a wide range in discrete steps

ABSTRACT

A tunable magnetron has, adjacent and spaced above each vane separating the cavities, an inductive tuner. Each inductive tuner is capable of being energized in order to occupy one of two predetermined positions, each position corresponding with a different tuned frequency. The frequency changes produced by actuation of the different inductive tuners is arranged such that the frequency changes produced by each tuner vary in accordance with a binary relationship.

O United States Patent 11 1 1 1 3,729,646 Pickering 1 1 Apr. 24, 1973 54 MAGNETRON TUNABLE BY PIEZO- 3,478,247 11/1969 Hull .315/3955 ELECTRIC MEANS OVER A WIDE 3,087,124 4/1963 McLeod, Jr. RANGE I DISCRETE STEPS 3,334,267 8/1967 Plumridge ..3l5/39.55 I 2,752,495 6/1956 Kroger ..315/39.55 X [75] Inven r: Al n g Plckermg, p g 3,440,565 4/1969 Scullin et a1... ..315/39.55 x Chelmsford, England 3,590,312 6/1971 Blank et a]. ..315/39.55 [73] Asslgnae: gz Company Primary E.\'aminerRud0lph V. Rolinec g Assistant ExuminerSaxfield C hatmon, Jr. [22] Filed: June 7, 1971 AtmrncyBaldwin, Wight & Brown A ppl. No.: 150,292

Foreign ApplicationPriority Data July 1, 1970 Great Britain 1.3l,939/70 1.5. C]. ..315/39.55, 315/3959, 315/3961 Int. Cl ..H0lj 25/50 Field of Search ..3l5/39.55, 39.61,

References Cited UNITED STATES PATENTS Perkins et a] ..3l5/39.55

I57] ABSTRACT A tunable magnetron has, adjacent and spaced above each vane separating the cavities, an inductive tuner. Each inductive tuner is capable of being energized in order to occupy one of two pre-determined positions, each position corresponding with a different tuned frequency. The frequency changes produced by actuation of the different inductive tuners is arranged such that the frequency changes produced by each tuner vary in accordance with a binary relationship 8 Claims, 2 Drawing Figures Patented April 24, 1973 2 Sheets-Sheet l Patented April 24, 1973 3,729,646

2 Sheets-Sheet 2 W 5m W 1 :ZZW

K M IORNLY."

MAGNETRON TUNABLE BY PIEZO-ELECTRIC MEANS OVER A WIDE RANGE IN DISCRETE STEPS This invention relates to magnetrons and has for its object to provide improved magnetrons which shall be rapidly variable in frequency within a wide range of frequencies.

It is a requirement in Radars for certain uses to be able to change the transmitted frequency rapidly over a wide range of frequencies. This may be required for example to reduce interference or to obtain improved reflected echoes from a target which is found to give poor echoes when one transmitted frequency is employed but better ones when another frequency is transmitted. The requirement also arises in those equipments in which change in the direction of transmission, e.g., for scanning space in azimuth or elevation, is obtained electrically by alteration of the frequency fed to a stationary aerial system instead of by rotating or swinging the aerial system mechanically about an axis. Variably tunable magnetrons in which the frequency is variable continuously by continuous adjustment of the position of a movable tuning member provided in the magnetron structure for example by moving a metal tuning member which is movable in relation to the magnetron anode system and is carried by a deformable diaphragm or bellows forming part of the evacuated envelope of the magnetron are well known. However, such known continuously tunable magnetrons leave much to be desired so far as satisfying the above-mentioned requirement is concerned. Among their disadvantages in this connection are that they are complex and, because of the nature of the mechanical movement required to be imparted to the tuning member and because of the inertia of the said member and of the means provided for moving it, the rapidity with which a change of frequency can be achieved over a wide range is severely limited. Indeed great difficulty is encountered, with known continuously tunable magnetrons, in achieving a desirably large range of frequency change at all. Moreover, in a Radar, the receiver tuning must be kept always aligned with the transmitter tuning receiver tuning is normally effected by a continuously tunable frequency changing local oscillator and the achievement of this presents very serious difficulty when known continuously tunable magnetrons are used because the tuning characteristics of such magnetrons are non-linear and very difficult to match with the tuning characteristic of the receiver in the manner necessary to maintain proper alignment during tuning. The present invention seeks to overcome these difficulties and provide tunable magnetrons which shall be more satisfactory for purposes such as those hereinbefore mentioned than are known tunable magnetrons.

According to this invention a tunable magnetron comprises a plurality of tuning devices each having two states providing two different tuned frequencies and control means for independently changing over the said states from one to the other, or vice versa, of said tuning devices individually, or in pre-determined combinations of devices.

The tuning devices may take any ofa variety of forms known per se, e.g., they could be movable metal members or movable dielectric members; or they could be constituted each by a conductive loop placed in a region of magnetron R.F. field, and equipped with switching means for opening and closing the loop to change frequency; or they could be constituted each by means for producing a gas or electron discharge which interacts with the RF. fields in the magnetron, change in frequency being effected by switching on or off the discharge.

Where change of state of a tuning device is achieved by mechanical movement of said device or of a member associated therewith the arrangement is preferably such that said device or member has two stable states of mechanical equilibrium. This, however, though preferred (it offers, among other advantages, excellent insensitivity to accidental variation of frequency due to mechanical shock or vibration) is not essential for the two states of tuning of each device can be obtained by quantitative control of the control means therefor.

Preferably the changes of frequency obtained by changing the states of the different tuning devices are different and in binary relationship. In other words, if one device, when changed in state produces a change ofx Mc/s, another is arranged to produce a change of 2x Mc/s, a third is arranged to produce a change of 4x Mc/s and so on. Thus, by changing the states of one or more tuning devices any of a plurality of different frequencies, differing from one another by x Mc/s and extending over a wide range, can be obtained.

The control means for changing the states of the tuning devices may take any of a wide variety of forms, e.g., they could be electric, hydraulic, pneumatic, mechanical, or piezo-electric (using a crystal, e.g., a ferro-electric crystal such as lead zirconate or barium titanate of sufficiently large capability of movement). The means adopted in any particular case will depend upon requirements and, obviously, where high speed tuning is required, they should be designed to be of minimum inertia. From this point of view piezo-electric control means are very good. However, there is no difficulty in achieving as high a speed of tuning as is likely to be desired. As already stated, the adoption of an arrangement in which use is made of movable members with two stable states of mechanical equilibrium is preferred. However, if desired, the arrangement may be such that each movable member is moved from one pre-determined position to the other by control means therefor arranged to exert one or other of two values of driving force. Thus if electrical control means are employed, an applied voltage of small value, e.g., one less than 0.5V, may be arranged to cause the member moved thereby to adopt one position while an applied voltage of considerably larger voltage, e.g., one of more than 10 volts, may be arranged to cause said member to adopt its other position. If each movable member has two stable states of mechanical equilibrium the control means therefor can obviously be arranged to be actuated by simple pulses, e.g., electrical pulses. In either case no requirement involving delicate quantitative control of the moving control means arises.

As will now be apparent the invention lends itself admirably to control of frequency by digital signals derived, for example, from a computer.

The tuning devices themselves may be fitted individually in different cavities of a conventional multicavity magnetron, e.g., a magnetron of the hole and slot type, or, in the case of a co-axial magnetron, at different points in the common resonator thereof.

In the case of a radar employing a tunable magnetron in accordance with this invention to provide the transmitted frequency, alignment of the tuning of the receiver can be achieved by means providing control, in steps, of the frequency of the frequency changing local oscillator of the receiver, said means being gauged and at least approximately aligned with the tuning control means of the magnetron. Approximate alignment of the tuning control means of the receiver will usually be sufficient because this will result in the receiver tuning being sufficiently closely aligned to enable the normally provided A.F.C. of the receiver to achieve and maintain the required more precise alignment.

The invention is illustrated in the accompanying drawings which show in schematic manner two of the many different forms in which the invention may be embodied. In both these forms the magnetron is exemplified as of the well known kind having an anode system with radial vanes. Only such parts of the magnetron are shown as is necessary to an understanding of the invention.

Referring to FIG. 1, the anode system of the magnetron therein represented comprises a main anode block cylinder 1 with radial vanes 2 and the usual straps" 3. Adjacent, spaced above, and extending over part of each vane is an inductive tuner constituted by an inductive metal shutter represented at 4. Only two of these shutters are shown but there will normally be one similarly associated with each vane. Each shutter 4 is carried by and is movable with respect to its associated vane 2 by a piezo-electric actuating or control element represented schematically at 5. Each piezoelectric actuator is arranged to produce sideways movement of its associated shutter 4 as indicated by the double-headed arrows X. Thus by energizing any particular piezo-electric actuator the shutter actuated thereby may be moved to one extreme position and will return to another when its actuator is de-energized. By employing for the actuators piezo-electric crystals capable of sufficient mechanical movement when energized, a suitable desired change of frequency of the magnetron can be obtained very rapidly by energizing or de-energizing any actuator. Suitable piezo-electric crystals are ferro-electric crystals such as lead zirconate or barium titanate. By appropriate design and arrangement of the shutters and their actuators it is possible (and in general, is preferred) to arrange the frequency changes produced by actuation of the different actuators to be different and in binary relationship.

Selective energization of any one or any selected plurality of the piezo-electric actuators is effected under the control of an electronic controller 6 which may be of any known kind adapted, under the control of digital or other control signals fed in from a computer or other source (not shown) over the input circuit 7, to select for energization the actuator or combination of actuators required to be selected to obtain the desired one of the selectable frequencies of oscillation of which the tunable magnetron is capable. It is assumed in FIG. 1 that the magnetron is to provide the transmitted frequency of a radar. Accordingly the electronic control unit 6 is also adapted to provide over an output circuit 8 digital or other control signals for controlling in steps the tuning of the normally provided local oscillator of the radar receiver (not shown) in such manner that when the magnetron is tuned to provide a particular frequency, the local oscillator is tuned to such a frequency as to tune the receiver at least approximately to the transmitted frequency. It is not'necessary that the receiver tuning effected by the unit 6 shall be precisely aligned with the transmitted frequency, it being sufficient if the said receiver tuning so effected is nearly enough correct for the normally provided receiver A.F.C. circuit to produce the required more precise alignment.

The magnetron shown in FIG. 2 is of the same type as that represented in FIG. 1 but tuning is effected-by a somewhat different arrangement which is, however, again piezo-electrically actuated. Only one tuning device is shown in FIG. 2 but in practice a similar tuning device will be provided in each of the magnetron cavities. These are, of course, each between two neighboring anode vanes 2.

The tuning device shown in FIG. 2 is essentially a device which, when actuated, partially short circuits the cavity in which it is situated. It consists of a switch composed of two parts 9 and 10, one attached to one and the other attached to the other of two adjacent vanes 2. The switch part 10 is flexible and in one of its positions contacts with the part 9 to complete a closed circuit between the two vanes, the ends of the two parts being provided with suitable co-operating contacts. The switch thus constituted is opened or closed by flexing the part 10 by means of an insulating rod 12 which passes through a suitable hole in the anode block cylinder 1 and is movable endwise by an over-center spring strip 11 which can adopt either of two stable positions, one of which is shown in full lines and the other in broken lines. The strip 11 is anchored at one end to a fixed anchorage l4 and at the other end is fixed to a piezo-electric actuator 13 adapted, when energized or tie-energized, to move said other end of the strip in one or other of the two directions indicated by the double headed arrow X and thus change over the strip 11 from one of its positions to the other to open or close the switch 9-10.

An arrangement as shown in FIG. 2 will normally be provided for each of the magnetron cavities. By suitable designing and arranging the different partial short circuiting devices in the different cavities it is possible to make the frequency changes produced by actuation of the different devices different and in binary relationship.

The piezo-electric actuators in FIG. 2 may be controlled in the manner already described in connection with FIG. 1 by means of an electronic controller which may also serve, again as described in connection with FIG. 1, to effect digital or similar control of the tuning of the local oscillator of a radar receiver, to tune the receiver in alignment with the transmitter of which the oscillator is the tunable magnetron shown in FIG. 2.

I claim: i

I. In a magnetron tunable at high rates over a wide frequency range, said magnetron including an anode structure presenting resonant cavity means, a plurality of discrete tuning devices each associated with said resonant cavity means and each capable of operation only at a first fixed state and at a second fixed state in which change from said first fixed state to said second fixed state and vice versa each occur within a given short period of time to produce a step-like frequency change of magnetron tuning, actuating means associated with each tuning device for actuating each such tuning device from either one of-its two states to the other state within said given short period of time, and control means connected to said actuating means for selectively operating said actuating means individually to provide different combinations of said tuning devices which are in the same state thereby to effect tuning of the magnetron in discrete steps within and over said wide frequency range.

2. In a magnetron as claimed in claim 1 wherein said tuning devices are constituted by movable metal members. 4

3. In a magnetron as claimed in claim 1 wherein each of said tuning devices has two stable states of mechanical equilibrium corresponding to said first fixed state and said second fixed state.

4. In a magnetron as claimed in claim 1 wherein each actuating means is responsive mom or other of two values of driving force from said control means.

5. In a magnetron as claimed in claim 4 wherein each of said actuating means is constructed of piezo electric material.

6. A magnetron as claimed in claim 1 wherein the changes of frequency obtained by changing the states of the different tuning devices are different and in binary relationship whereby changing the states of one or more tuning devices any of a plurality of different frequencies, differing from one another by a pre-determined amount of frequency and extending over a wide range, can be obtained.

7. In a magnetron as claimed in claim 1 wherein said anode structure comprises an anode block cylinder and a plurality of vanes extending radially inwardly of said cylinder, each tuning device comprising a metal shutter overlying one of the cylinder and a portion of an associated one of said vanes.

8. In a magnetron as claimed in claim 1 wherein said anode structure comprises an anode block cylinder and a plurality of vanes extending radially inwardly of said cylinder, each tuning device comprising a switch, each switch being located between a different pair of radial vanes and connected thereto for selectively short circuiting therebetween. 

1. In a magnetron tunable at high rates over a wide frequency range, said magnetron including an anode structure presenting resonant cavity means, a plurality of discrete tuning devices each associated with said resonant cavity means and each capable of operation only at a first fixed state and at a second fixed state in which change from said first fixed state to said second fixed state and vice versa each occur within a given short period of time to produce a step-like frequency change of magnetron tuning, actuating means associated with each tuning device for actuating each such tuning device from either one of its two states to the other state within said given short period of time, and control means connected to said actuating means for selectively operating said actuating means individually to provide different combinations of said tuning devices which are in the same state thereby to effect tuning of the magnetron in discrete steps within and over said wide frequency range.
 2. In a magnetron as claimed in claim 1 wherein said tuning devices are constituted by movable metal members.
 3. In a magnetron as claimed in claim 1 wherein each of said tuning devices has two stable states of mechanical equilibrium corresponding to said first fixed state and said second fixed state.
 4. In a magnetron as claimed in claim 1 wherein each actuating means is responsive to one or other of two values of driving force from said control means.
 5. In a magnetron as claimed in claim 4 wherein each of Said actuating means is constructed of piezo electric material.
 6. A magnetron as claimed in claim 1 wherein the changes of frequency obtained by changing the states of the different tuning devices are different and in binary relationship whereby by changing the states of one or more tuning devices any of a plurality of different frequencies, differing from one another by a pre-determined amount of frequency and extending over a wide range, can be obtained.
 7. In a magnetron as claimed in claim 1 wherein said anode structure comprises an anode block cylinder and a plurality of vanes extending radially inwardly of said cylinder, each tuning device comprising a metal shutter overlying one end of the cylinder and a portion of an associated one of said vanes.
 8. In a magnetron as claimed in claim 1 wherein said anode structure comprises an anode block cylinder and a plurality of vanes extending radially inwardly of said cylinder, each tuning device comprising a switch, each switch being located between a different pair of radial vanes and connected thereto for selectively short circuiting therebetween. 